Methods and apparatus for storage area network component registration

ABSTRACT

The invention provides, in one aspect, a digital data processing system having an interconnect that provides for registration of components communicating thereon. One or more host devices, storage devices or other components are coupled to the interconnect for communication, at least one of them lacking an ability to self-register with the interconnect. Such a component is referred to herein as a non-compliant component. A registration module coupled with the interconnect performs the registration on behalf of the non-compliant component.

BACKGROUND OF THE INVENTION

[0001] The invention pertains to digital data processing and, more particularly, to networks and methods of operation thereof. The invention has application, for example, in managing storage area networks.

[0002] In early computer systems, long-term data storage was typically provided by dedicated storage devices, such as tape and disk drives, connected to a data central computer. Requests to read and write data generated by applications programs were processed by special-purpose input/output routines resident in the computer operating system. With the advent of “time sharing” and other early multiprocessing techniques, multiple users could simultaneously store and access data—albeit only through the dedicated storage devices.

[0003] With the rise of the personal computer and workstation in the 1980's, demand by business users led to development of interconnection mechanisms that permitted otherwise independent computers to access data on one another's storage devices. Though computer networks had been known prior to this, they typically permitted only communications, not storage sharing.

[0004] The prevalent business network that has emerged is the local area network, typically comprising “client” computers (e.g., individual PCs or workstations) connected by a network to a “server” computer. Unlike the early computing systems in which all processing and storage occurred on a central computer, client computers usually have adequate processor and storage capacity to execute many user applications. However, they often rely on the server computer—and its associated battery of disk drives and storage devices—for other than short-term file storage and for access to shared application and data files.

[0005] An information explosion, partially wrought by the rise of the corporate computing and, partially, by the Internet, is spurring further change. Less common are individual servers that reside as independent hubs of storage activity. Often many storage devices are placed on a network or switching fabric that can be accessed by several servers (such as file servers and web servers) which, in turn, service respective groups of clients. Sometimes even individual PCs or workstations are enabled for direct access of the storage devices (though, in most corporate environments such is province of server-class computers) on these so-called “storage area networks” or (SANs).

[0006] The management of SANs typically involves automated discovery of the SAN physical topology, e.g., the interconnections and relationships among host computers (e.g., servers), storage devices and other components participating in the SAN, and their configurations. This can be accomplished through in-band discovery—that is, by querying designated addresses in the devices or on the network or fabric that connects them. However, the information provided by most in-band discovery mechanisms is limited to how the components' respective physical network end-points, or ports, are connected. Referring to FIG. 1, for example, in-band discovery might reveal that there are a number of ports connected into the SAN fabric, but it will not reveal in which of those host computers (Host 1, Host 2 or Host 3) the ports are contained.

[0007] The art has taken steps toward facilitating SAN management, e.g., in instances where only in-band discovery is possible. An emerging industry standard T11/FC-GS-3 of the American National Standard of Accredited Standards Committee NCITS, for example, proposes a system of “platform” registration, wherein each component (or platform) on a fibre channel fabric registers with a fabric-based service, supplying information such as component name and type, contained fibre channel ports, management addresses, description and location. That information is made available to the other components which can use it, e.g., for storage area network management.

[0008] Though platform registration can facilitate SAN management, many SAN components do not practice it. This will likely be the state of affairs for many years to come as manufacturers bring their fibre channel and non-fibre channel (e.g., iSCSI) product lines into conformity with registrations standards such as those provided under T11/FC-GS-3.

SUMMARY OF THE INVENTION

[0009] The foregoing are among the object attained by the invention which provides, in one aspect, a digital data processing system having an interconnect that provides for registration of components communicating thereon. One or more host devices, storage devices or other components are coupled to the interconnect for communication, e.g., of commands, data and other information. At least one of the components lacks an ability to self-register with the interconnect and is referred to herein as a non-compliant component. A registration module executing on a digital data processor that is coupled with the interconnect via one (or more) of the components performs the registration on behalf of the non-compliant component.

[0010] Related aspects of the invention provide a digital data processing system as described above in which the interconnect operates in accord with a fibre channel protocol. Further related aspects of the invention provide such a system in which the fibre channel interconnect comprises one or more elements, e.g., switches, that define a configuration server that provides the aforesaid registration.

[0011] Other aspects of the invention provide a digital data processing system as described above in which the registration module obtains registration information for a non-compliant component from a system administrator or other user (hereinafter, “system administrator”). Related aspects of the invention provide such a system in which the information obtained by the registration module from the administrator includes a name and type of the non-compliant component, as well as a management address list and a node list therefor. Still further related aspects of the invention provide such a system in which that information is obtained from the administrator via a graphical or other user interface provided by a storage area network manager executing on a digital data processor common to the registration module.

[0012] In other aspects, the registration module of a system as described above communicates registration information with the interconnect via the storage area network manager and particularly, by way of example, via an agent of the manager executing on one of the components.

[0013] In still other aspects, the invention provides a digital data processing system as described above which executes within one of the aforesaid components, communicating with a registration service in the interconnect via the component's host bus adapter. Further aspects of the invention provide a system as described above in which the registration module obtains information necessary to register a non-compliant component from pre-programmed setting and/or from a database. In further related aspects, the registration module can utilize a display console to obtain information from a system administrator for purposes of updating such a database.

[0014] Additional aspects of the invention provide a registration module for use in a digital data processing system of the type described above.

[0015] Still other aspects of the invention provide methods of operating a digital data processing system and/or registration module in accord with the above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 depicts a storage area network architecture according to the prior art;

[0017]FIG. 2 depicts a storage area network (SAN) embodying a manual registration module according to the invention;

[0018]FIG. 3 depicts communication between a registration module of the FIG. 2 and a fibre channel interconnect; and

[0019]FIG. 4 depicts an automated registration module according to the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

[0020]FIG. 2 illustrates an exemplary storage area network (SAN) 10 embodying the invention in which one or more components-including one or more hosts 12 a-12 c and/or one or more storage devices 14 a-14 n—communicate with one another via an interconnect fabric 16 having a plurality of interconnect elements, such as, switches 16 a-16 c. In addition to hosts 12 and storage devices 14, gateways (not shown) and other digital data devices of the type known in the art may be coupled to the interconnect fabric 16.

[0021] Illustrated hosts 12 are typically web servers, application servers or file servers (e.g., for client computers not shown in the drawing), graphical workstations and so forth, though they may comprise any digital data devices that access and/or store (collectively, “access”) information on the storage devices 14. The hosts 12 are constructed and operated in the conventional manner, as modified in accord with the teachings herein.

[0022] Illustrated storage devices 14 comprise apparatus for storing and/or retrieving data. These typically comprise disk drives and arrays of the type conventionally used in storage area networks, though any variety of storage devices (e.g., tape libraries) may be used for this purpose. By way of non-limiting example, the illustrated devices may comprise, or form parts of, storage subsystems, storage servers, storage virtualization systems. Regardless, the storage devices 14 are constructed and operated in the conventional manner, as modified in accord with the teachings herein.

[0023] The illustrated SAN includes a manager 20 that provides administrative services with respect to SAN 10. This includes network component discovery, topology reporting, event monitoring, device manager launching and/or network configuration. SAN manager 20 executes on a general purpose or server workstation; though it may be implemented on any general or special purpose digital data device known in the art. A preferred SAN manager 20 is a fibre channel network manager of the type disclosed in copending, commonly assigned application U.S. Ser. No. 09/972,584, entitled “Storage Area Network Methods And Apparatus With Centralized Management,” filed Oct. 5, 2001, the teachings of which are incorporated herein by reference. Other network managers, whether commercially available or otherwise, capable of providing services with respect to SAN 10 may be used in addition or instead.

[0024] The SAN manager 20 may be coupled directly to the interconnect fabric 16. However, as shown in FIG. 3, in the illustrated embodiment, communications between manager 20 and fabric 16 take place via modules, referred to as agents in incorporated-by-reference application U.S. Ser. No. 09/972,584, residing on one or more of the hosts 12. Those agents communicate with the interconnect through the host bus adapters (HBAs), or other interconnect interfaces, of the respective hosts, e.g., to gather information from, and apply commands and information to, the interconnect on behalf of the manager 20.

[0025] A further appreciation of this two-tier mechanism for communication between SAN manager 20 and the interconnect 16 via an agent (or agents) residing on host(s) 12 (e.g., utilizing agent gateway and IP communications link (or other communications connection), all as illustrated in FIG. 3) may be attained by reference to incorporated-by-reference application, U.S. Ser. No. 09/972,584 and particularly, by way of non-limiting example, by reference to FIGS. 4-6 and 36, and the accompanying text thereof, all incorporated by reference herein.

[0026] Other embodiments of the invention may utilize alternative mechanisms known in the art to support communications between the SAN manager 20 and the interconnect 16 via the hosts 12 or components on the interconnect 16.

[0027] Illustrated console 24 facilitates access by a user or system administrator (hereinafter, “administrator”) to the SAN manager 20. This is typically a personal computer or workstation and, indeed, may be the same device on which the SAN manager 20 is embodied. In addition to a processor, the console 24 comprises a display, keyboard and/or other input/output devices (such as a mouse and printer). Other human machine interface (HMI) devices of the variety known in the art may be used in addition or instead (e.g., personal digital assistants, teletype terminals, touch pads, and so forth).

[0028] SAN manager 20 utilizes a graphical user interface (GUI) to drive information to the console 24 and/or collect information therefrom. For example, the manager 20 employs the GUI to present a topological display of SAN components 12, 14 and interconnect elements 16 a-16 c on the console 24. The GUI can likewise be used to present and collect information in regard the provisioning of other services by SAN manager 20 with respect to SAN 10.

[0029] Illustrated interconnect 16 comprises a fibre channel fabric, including fibre channel media, switches 16 a-16 c, and other elements necessary, typical and/or otherwise used to provide fibre channel connectivity between the illustrated devices 12, 14. In alternative embodiments, interconnect 16 utilizes other fabrics, networks or other communications media for transfers between hosts 12 and devices 14. These include interconnects operating in accord with internet protocol and a variety of other protocols known or to be known in the art.

[0030] The constituent elements of illustrated fibre channel interconnect 16 define a configuration server 18 of the type contemplated under fibre channel standard T11/FC-GS-3, e.g., as defined in NCITS xxx-200x T11/Project 1356-D/Rev 7.01 (Nov. 28, 2000), promulgated by the American National Standard for Information Technology, hereinafter referred to as the “fibre channel specification,” at Section 6.1, the teachings of which are incorporated herein by reference. One or more other services defined under the standard, e.g., directory services, other management services, time services, alias services and key distribution service, may be provided by these or other elements as well. Though depicted as being provided by switches 16 a-16 c, those skilled in the art will appreciate that the configuration server and/or any of the other services contemplated by the aforementioned standard may be provisioned by other elements of the interconnect 16 as well, and, indeed, by the hosts 12, storage devices 14, server 20 or other components of the SAN.

[0031] With respect to the illustrated embodiment, the term “component” refers to a host 12, storage device or other digital data device that is coupled to the interconnect via a node and its associated ports. In this regard, “component” is synonymous with the term “platform device,” as used in the fibre channel specification. In embodiments where the interconnect 16 is other than fibre channel, the term “component” refers to digital data devices (again, such as hosts, storage devices and so forth) that couple for communication with the respective interconnects. With further respect to the illustrated embodiment, the term “element” refers to devices that form the interconnect fabric 16. In this regard, “element” is synonymous with “Fibre Channel component,” as used in the fibre channel specification. In embodiments where the interconnect 16 is other than fibre channel, the term “element” correspondingly refers to devices that make up the respective interconnects.

[0032] Per the fibre channel specification, components on a fibre channel interconnect (such as interconnect 16) are intended to self-register with the configuration server so that management applications, such as SAN manager 20, can discover the SAN topology and attributes. To this end, self-registering (or compliant) components issue appropriate platform registration commands to the interconnect 16, e.g., the RPL Fabric Configuration Server request detailed in the fibre channel specification at Section 6.1.4.23, providing requisite parameters for registration, e.g., the following parameters also detailed in the aforementioned section of the fibre channel specification: Short Name (per Figure 2 Parameter (per fibre channel specification) hereof) CT_IU preamble Platform Name “Name” Platform Type “Type” Number of Management Address entries “Management Address List” (n) Management Address #1 Management Address #2 . . . Management Address #n Number of Platform Node Name entries “Node List” (n) Platform Node Name #1 Platform Node Name #2 . . . Platform Node Name #n

[0033] The configuration server makes this information available, in turn, upon request of any component on the interconnect fabric. In the illustrated embodiment, such requests are issued, for example, by the agents on behalf of the SAN manager 20, e.g., during in-band discovery.

[0034] Manual Platform Registration

[0035] In the illustrated embodiment, a novel manual registration module 22 attends to registration of hosts 12, storage devices 14 and other components of the SAN that are not capable (or do not otherwise) self-register with the configuration service (referred to below as “non-compliant” components). The module 22 beneficially executes on the same digital data processor as the SAN manager 20 and, indeed, can be packaged for installation and execution therewith. In other embodiments, the module 22 can be execute on other digital data devices (not shown) that communicates to the interconnect 16 via hosts 12 or other components on that interconnect 16. Illustrated manual platform registration module 22 is coupled with the console 24 associated with SAN manager 20 (and, specifically, via SAN Manager Console GUI shown in FIG. 3 and described, in further detail, in incorporated-by-reference application, U.S. Ser. No. 09/972,584 and particularly, by way of non-limiting example, in FIGS. 4-6 and 36, and the accompanying text thereof) and utilizes the aforementioned GUI to present information to the administration and accept input therefrom. In alternative embodiments, the module utilizes a separate display and/or graphical (or other) interface functionality.

[0036] Because it need not directly interface the interconnect 16 and its constituent configuration server 18—relying, instead, on hosts 12 or other SAN components for that purpose—implementation and operation of module 22 is greatly facilitated. This proves further true where, as in the illustrated embodiment, the module 22 relies on the GUI provided by manager 20 (or other digital data devices) and console 24 to interface with the operator.

[0037] The module 22 can be invoked by the administrator (e.g., via a menu option on the SAN manager 20 or otherwise), automatically (e.g., in response to detection by SAN manager 20 of addition of a component to the SAN), or otherwise, to register a component in the first instance or to modify the parameters of a previously registered component. It can likewise be invoked to cancel a component registration.

[0038] As depicted in FIG. 2, module 22 utilizes the console 24 to obtain from the administrator information concerning a host 12, storage device 14 or other non-compliant component to be registered. Specifically, it obtains for the component to be registered the name, type, node list, and management address list, which correspond to parameters expected in the configuration server as indicated in the table above. That information is communicated to a host 12 agent, along with an 20 indication that it is to be included in an RPL Fabric Configuration Server command (or other such command) for issuance to the interconnect 16. The agent, in turn, issues the RPL Fabric Configuration Server command (or other such command), for entry of the information into the configuration server 18. This has the effect of registering the non-compliant component with the fibre channel interconnect 16, e.g., as if that component had registered itself with the server 18.

[0039] Information for the non-compliant component may henceforth be obtained by other components from configuration server 18 in the usual manner, e.g., through issuance of queries to the server 18. Among other benefits, this facilitates discovery and management of non-compliant components, e.g., in instances where only in-band discovery is possible. By way of example, components querying the interconnect 16 subsequent to registration of a non-compliant component (by module 22) can obtain information from the server 18 to determine not only how the physical network endpoints, or ports, are connected but also which hosts 12 or storage devices 14 those ports are contained in.

[0040] Automatic Platform Registration

[0041] In addition to, or instead of, manual registration, some embodiments of the invention provide for automatic platform registration. Referring to FIG. 4, automated platform registration module 26 comprises “agent” or other process that executes directly on a host 12. In the illustrated embodiment, this is a stand-alone process, though, it can form part of and/or execute in connection with an aforementioned agent tier of the SAN manager 20. In some embodiments, the automated platform registration module 26 commences operation on boot-up of the host 12 on which it resides, performs registration, then terminates. Though intended for execution on host-type SAN components, e.g., servers, workstations and other digital data processors, the automated platform registration module 26 can execute on other types of SAN components, e.g., storage devices, e.g., via an embedded operating system, or otherwise.

[0042] Illustrated module 26 obtains from pre-programmed default settings and/or from a persisted database 28 (or other store) registration parameters for the local host 12 (i.e., the host on which the module resides) and/or one or more other non-compliant hosts 12, devices 14 or other SAN components. To the extent database 28 is used, information contained in it can be preset or it can derive from information entered by the administrator, e.g., upon installation of each respective component, or obtained otherwise (e.g., from a manufacturer's or service provider's web site). To facilitate entry of such information into the database by the administrator, a graphical user interface 30 can be supplied which presents displays (e.g., of the sort depicted in FIG. 2) on a console (not illustrated) and obtains from the administrator requisite parameters for each non-compliant component for which registration information is to be persisted in the database 28.

[0043] Regardless, the module 26 obtains (from the database, from preprogrammed defaults or otherwise) for each component to be registered the name, type, node list, and management address list, which correspond to parameters expected in the configuration server as indicated in the table above. As with the manual registration module 22, the module 26 formats the information as necessary per the fibre channel specification and issues RPL Fabric Configuration Server or other commands for its entry into the configuration server 18. From that point onward, the SAN manager 20 (or other requester coupled to the fabric 16) can obtain information regarding the otherwise non-compliant component as if it had registered itself in accord with the fibre channel specification. Communications between the automatic registration module 26 and the configuration server 18 can be handled via the local host 12 HBA in the conventional manner.

[0044] Described above are methods and apparatus for registering hosts, storage devices and other non-compliant SAN components with a platform registration service of the type discussed, for example, in the aforementioned fibre channel specification. Those skilled in the art will appreciate that the invention has application beyond SAN components and can be extended, for example, to elements of the fabric 16, such as switches, gateways, and the like. Moreover, it will be appreciated that the invention can be applied to storage area and other networks that operate with protocols other than fibre channel. In view of the foregoing and understanding that the illustrated embodiments are merely examples of the invention, and further understanding that apparatus and methods incorporating modifications thereto fall within the scope of the invention, what we claim is: 

1. A digital data processing system of comprising an interconnect that provides for registration of components communicating thereon, one or more components coupled to the interconnect for communication thereon, at least a one of the components lacking an ability to self-register with the interconnect, such a component being referred to herein as a non-compliant component, a digital data device that is coupled with at least a selected one of the components, the digital data device registering, via communications through the selected component, a non-compliant component with the interconnect.
 2. A digital data processing system according to claim 1, wherein each component comprises any of host device, storage device, or other digital data device.
 3. A digital data processing system according to claim 1, wherein the interconnect operates in accord with a fibre channel protocol (FCP).
 4. A digital data processing system according to claim 3, wherein the interconnect comprises one or more elements defining a configuration server that provides the aforesaid registration.
 5. A digital data processing system according to claim 1, wherein the digital data device executes a registration module that obtains registration information for a non-compliant component from a system administrator or other user (hereinafter, “system administrator”).
 6. A digital data processing system according to claim 5, wherein the information comprises one or more of a component name, a component type, a management address list, and a node list.
 7. A digital data processing system according to claim 5, wherein the information comprises each of a component name, a component type, a management address list, and a node list.
 8. A digital data processing system according to claim 5, wherein the registration module obtains the information from the system administrator via a console or other human-machine interface.
 9. A digital data processing system according to claim 5, comprising a further registration module that registers non-compliant components, the further registration module executing within one of the components.
 10. A digital data processing system according to claim 9, wherein the further registration module executes upon start-up of the component within which it executes.
 11. A digital data processing system according to claim 9, comprising a store that is coupled to the further registration module and that maintains one or more of a component name, a component type, a management address list, and a node list for at least one non-compliant component.
 12. A digital data processing system according to claim 11, wherein the store comprises each of a component name, a component type, a management address list, and a node list for the non-compliant component.
 13. A digital data processing system according to claim 11, wherein the further registration module registers a non-compliant component by supplying to the component registration service the component name, component type, management address list, and/or node list for that non-compliant component.
 14. A digital data processing system according to claim 11, wherein the further registration module obtains the component name, component type, management address list, and/or node list from the system administrator via a console or other human-machine interface.
 15. A digital data processing system according to claim 14, wherein the further registration module updates the store with the component name, component type, management address list, and/or node list from the system administrator.
 16. In storage area network of the type having an interconnect that provides for registration of components communicating thereon, one or more components coupled to the interconnect for communication thereon, a network manager that is coupled to the interconnect and that provides administrative services with respect to the storage area network based on registration information from the interconnect, the improvement wherein the network manager executes on a selected digital data processor that is coupled with at least a selected one of the components, the network manager transferring information with the interconnect via the selected component, a registration module executes on the selected digital data processor, the registration module (i) obtaining from a system administrator or other user (hereinafter, “system administrator”) information regarding a component that is coupled to the interconnect and that lacks an ability to self-register with the interconnect, (ii) applying that information to the network manager for transfer to the interconnect via the selected component for purposes of registering the non-compliant component.
 17. In a storage area network according to claim 16, the further improvement wherein the interconnect operates in accord with a fibre channel protocol (FCP).
 18. In a storage area network according to claim 17, the further improvement wherein the interconnect comprises one or more elements defining a configuration server that provides the aforesaid registration.
 19. In a storage area network according to claim 16, the further improvement wherein the network manager provides at least one of discovery, topology reporting, event monitoring, device manager launching and/or network configuration.
 20. In a digital data processor according to claim 19, the further improvement wherein at least the selected component comprises an agent that interfaces with the interconnect via a host bus adapter of the respective component.
 21. In a digital data processor according to claim 20, the further improvement wherein the selected component communicates information with the interconnect on behalf of the network manger.
 22. In a digital data processor according to claim 16, the further improvement wherein the registration module obtains information from the system administrator via a user interface associated with the network manager.
 23. In a digital data processor according to claim 16, the further improvement comprising a further registration module that registers non-compliant components, the further registration module executing within one of the components.
 24. In a digital data processor according to claim 23, the further improvement wherein the further registration module executes upon start-tip of the component within which it executes.
 25. In a digital data processor according to claim 23, the further improvement comprising a store that is coupled to the registration module and that maintains one or more of a component name, a component type, a management address list, and a node list for at least one non-compliant component.
 26. In a digital data processor according to claim 25, the further improvement wherein the store comprises each of a component name, a component type, a management address list, and a node list for the non-compliant component.
 27. In a digital data processor according to claim 25, the further improvement wherein the further registration module registers a non-compliant component by supplying to the component registration service the component name, component type, management address list, and/or node list for that non-compliant component.
 28. In a digital data processor according to claim 25, the further improvement wherein the registration module obtains the component name, component type, management address list, and/or node list from the system administrator via a console or other human-machine interface.
 29. In a digital data processor according to claim 28, the further improvement wherein the registration module updates the store with the component name, component type, management address list, and/or node list from the system administrator.
 30. A method of digital data processing comprising communicating between a plurality of components over an interconnect that provides for registration of components communicating thereon, where the components comprising any of host devices, storage devices, or other digital data devices, and where at least a one of the components lacks an ability to self-register with the interconnect, such a component being referred to herein as a non-compliant component, registering a non-compliant component with the interconnect, the registering step being effected using a digital data device that is coupled with at least a selected one of the components and being effected via communications through the selected component.
 31. A method according to claim 30, wherein the interconnect operates in accord with a fibre channel protocol (FCP).
 32. A method according to claim 31, wherein the interconnect comprises one or more elements defining a configuration server that provides the aforesaid registration.
 33. A method according to claim 30, wherein the registering step includes obtaining registration information for a non-compliant component from a system administrator or other user (hereinafter, “system administrator”).
 34. A method according to claim 33, wherein the information comprises one or more of a component name, a component type, a management address list, and a node list.
 35. A method according to claim 33, wherein the information comprises each of a component name, a component type, a management address list, and a node list.
 36. A method according to claim 33, wherein the registering step includes obtaining the information from the system administrator via a console or other human-machine interface.
 37. A method according to claim 33, comprising operating a component to effect registration of a further non-compliant component.
 38. A method according to claim 37, comprising performing the operating step upon start-up of the component that effects that step.
 39. A method according to claim 37, comprising providing a store that is coupled to the further registration module and that maintains one or more of a component name, a component type, a management address list, and a node list for at least one non-compliant component.
 40. A method according to claim 39, wherein the store comprises each of a component name, a component type, a management address list, and a node list for the non-compliant component.
 41. A method according to claim 39, wherein the operating step includes supplying to the interconnect the component name, component type, management address list, and/or node list for that non-compliant component.
 42. A method according to claim 39, wherein the operating step includes obtaining the component name, component type, management address list, and/or node list from the system administrator via a console or other human-machine interface.
 43. A method according to claim 42, comprising updating the store with the component name, component type, management address list, and/or node list from the system administrator. 